1. Field of the Invention
This invention relates to apparatus for forming glass sheets with major and minor curvatures that are generally perpendicular to each other.
2. Background Art
U.S. Pat. Nos. 5,498,275, 5,556,444, and 5,697,999 of Reunamaki and U.S. Pat. No. 6,378,339 Zelesak disclose a glass sheet forming system for forming heated glass sheets during conveyance along a direction of movement of the glass sheet through the system. The forming is provided by lower and upper sets of deformable rolls that are vertically aligned with each other along the direction of conveyance and supported by associated members that are movable to move the lower and upper sets of rolls between a flat condition for receiving a heated glass sheet from an associated furnace and a curved condition for forming the glass sheet to a curved shape along a direction transverse to the direction of conveyance. Other glass sheet forming that is performed during movement of the glass along a direction of conveyance is disclosed by U.S. Pat. No. 4,883,527 McMaster et al. and U.S. Pat. No. 5,009,693 Freidel et al.
The above prior art has primarily been utilized in the past to provide cylindrical curvature without any cross bending transverse to the major axis of bending. However, for some period of time, vehicle design requirements have glass sheet shapes that incorporate cross curvature with major and minor axes of curvature. Such cross curvature has been provided by press bending apparatus wherein a flat glass sheet is shaped between complementary press molds to provide both a major axis of curvature and cross bending about a minor axis of curvature. For example, vehicle side windows having a length of about 1,200 millimeters (about 39 inches) will have a major axis of forming about a longitudinal vehicle direction and will have cross bending about a vertically inclined axis. Such cross bending normally has a radius of curvature of about 30 meters and is thus relatively slight in comparison to the major curvature. More specifically, for a glass part having a length of 1,200 millimeters (about 46 inches), cross bending with a 30 meter radius of curvature provides a depth of curvature from a straight line between the opposite ends of the part to the glass of only about three to four millimeters. Nevertheless, such cross curvature provides compliance with design shapes as well as providing good optical appearance and structural requirements of the completed part.